194 NATURAL SCIENCE [September 
Ophthalmosaurus tcenicus (R. 2137), described and figured by Seeley 
(Proce. Roy. Soc., vol. liv., 1893, fig. 1, p. 151). No such difficulty 
beset the restoration of the pelvis, since the parts are hardly at all 
displaced in specimen (41849). 
The diagram of the Plesiosaur is mainly based on the splendid 
specimen of Plesiosaurus rostratus from the Lower Lias of Char- 
mouth, Dorsetshire, exhibited in the Geological Gallery of the 
Museum, and bearing the register number (38525). This specimen 
was described and figured by Owen in his “ Liassic Reptilia” 
(Sauropterygia, 1865, pl. 9), but it did not form the basis of his 
well-known text-book restoration of Plesiosawrus (“ Anat. of Vert.,” 
vol. 1, 1866, p. 52), the species of which, according to Lydekker 
(Brit. Mus, Cat. Foss. Rept., part ii., 1889, p. 121), is macrocephalus. 
The number of cervical vertebrae in Plesiosawrus rostratus is not 
definitely known. Owen put it down as twenty-four, but there 
were probably more, since in the specimen (38525) there are 
evidently some vertebrae missing after the seventeenth (see 
Lydekker, Joc. cit., p. 272). Judging from the shape and relations 
of the cervical ribs flexion of the neck must have been as difficult 
of achievement in Plesiosaurus as in our modern crocodiles, and so 
the vertebral column in the cervical region has been drawn nearly 
straight (Fig. 3), instead of being allowed the graceful sinuous curve 
which characterises Owen’s figure. The outline of the body has 
been introduced from the figure given by Dames (Abhandl. kénigl. 
Akad. Wiss., Berlin, 1895, ii, p. 79) ; and special attention may be 
called to the shape of the tail fin, and to the presence of an integu- 
mentary extension of the paddle behind the part supported by the 
internal skeleton. The transverse temporal ridge at the back of 
the skull would probably not have influenced the general contour of 
the body to the extent suggested by the diagram. This improba- 
bility should have been avoided by making the vertebral column 
articulate a little higher up the occiput, and by putting the cranial 
axis more in a line with the cervical vertebrae. 
The cranium of the specimen above mentioned is considerably 
crushed ; therefore, while preserving the proportions of the cranial 
bones of this species, the actual details were added from the more 
perfect skull (49202) of the allied species P. macrocephalus, de- 
scribed and figured by Andrews (Quart. Journ. Geol. Soc., vol. lii., 
1896, pp. 246-253, pl. 9). The skeleton of the paddles in the 
specimen of Plesiosaurus rostratus is extremely well preserved, and 
nothing more was necessary than to copy the outlines of the 
constituent bones; but as the bones of the pectoral and pelvic 
girdles are disturbed, a certain amount of restoration was here 
inevitable, and the assistance derived from the perfect girdles of 
Muraenosaurus plicatus (R. 2428) and Cryptoclidus oxoniensis 
